1. Field of the Invention
The present invention relates to a vibration damping device adapted for installation between components to be provided with vibration damped linkage, and particularly to a fluid filled type vibration damping device that utilizes vibration damping action based on the flow action of a sealed therein.
2. Description of the Related Art
In the field of vibration damping devices such as vibration damping linkages or vibration damping supports designed for installation between components that make up a vibration transmission system, one type of known device is a fluid filled type vibration damping device that utilize vibration damping action based on the flow action of a fluid sealed inside. Such a fluid filled type vibration damping device has a first mounting member and a second mounting member linked by a rubber elastic body. To the inner peripheral side of the second mounting member, there is defined a pressure receiving chamber whose wall is partially constituted by the main rubber elastic body, and an equilibrium chamber whose wall is constituted by a flexible film. The chambers are filled with a non-compressible fluid, and the pressure receiving chamber and the equilibrium chamber communicate with each other through an orifice passage.
Based on the flow action of a fluid induced to flow between the pressure receiving chamber and the equilibrium chamber through the orifice passage, excellent vibration damping action can be produced against vibration in a specific targeted frequency range. The application of such fluid filled type vibration damping devices in automotive engine mounts, body mounts, and suspension mounts for example, is a topic of ongoing research. Japanese unexamined Patent Publication No. JP-A-8-28623 shows one example of a fluid filled type vibration damping device.
The known fluid filled type vibration damping devices are designed to exhibit vibration damping effect based on the flow action of a fluid against vibration in a narrow frequency range to which the orifice passage has been tuned. Therefore, they may suffer from a problem that effective vibration damping action will not be attained against vibration to be damped depending on errors in frequency of vibration to be damped, and individual difference in tuning of orifice passages due to manufacturing errors, dimensional errors, material errors and so forth of the fluid filled type vibration damping devices.
In recent years, one improvement of vibration damping ability is desired in order to exhibit higher attenuating action in a specific narrow frequency band, whereas there is increasingly higher requirements for another improvement of vibration damping ability in order to exhibit effective vibration damping action stably against vibration over a wider frequency range. That is, there exists a need for broadening vibration damping characteristics for effective attenuating action based on the flow action of the fluid through the orifice passage against vibration over a wider frequency range and stably exhibiting excellent vibration damping ability of fluid filled type vibration damping devices.
However, it is difficult for fluid filled type vibration damping devices of known construction to exhibit vibration damping effect based on the flow action of the fluid through the orifice passage over a wide frequency range, although they are able to adjust tuning frequency by means of appropriately setting the ratio of passage length and passage cross sectional area of the orifice passages etc. In particular, the fluid filled type vibration damping devices of simple construction without outside control mechanism such as electromagnetic oscillation members have not yet been realized the art that attains both effective vibration damping effect and effective wide frequency range at the same time.